The present invention relates to seals in a gas turbine for supplementing the chordal hinge seals between turbine nozzles and a turbine nozzle support ring and particularly relates to supplementary seals for substantially minimizing or eliminating leakage losses past the chordal hinge seals.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
In an exemplary arrangement, eighteen cast segments are provided with two vanes per segment. The annular array of segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between a high pressure region radially inwardly of the inner band, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure.
Chordal hinge seals are used to seal between the inner band of the first-stage nozzles and an axially facing surface of the nozzle support ring. Each chordal hinge seal includes an axial projection which extends linearly along a chordline of the inner band portion of each nozzle segment. Particularly, the chordal hinge seal extends along an inner rail of each segment and which rail extends radially inwardly of the inner band portion. The chordal hinge seal projection lies in sealing engagement with the axially opposite facing sealing surface of the nozzle support ring.
During operation and/or repair of the first-stage nozzle, it has been found that warpage can leave gaps between the chordal hinge seals and the sealing surface of the nozzle support ring. These gaps enable leakage past the chordal hinge seals from the high pressure area radially within the annular inner band into the hot gas flow path. That is, the chordal hinge seals are inadequate to prevent leakage flow as the chordal hinge seal projections lose contact with the sealing surface of the nozzle support ring. Consequently, there is a need for a supplemental seal at the interface of the first-stage nozzles and nozzle support ring to minimize or eliminate the leakage flow past the chordal hinge seals.
In accordance with a preferred embodiment of the present invention, there is provided a supplemental seal between the first-stage nozzles and the nozzle support ring which eliminates or minimizes leakage past the chordal hinge seals and which is readily and easily installed. In a preferred embodiment, the supplemental seal includes at least one and preferably two back-to-back sheet metal shims wrapped in a woven metallic cloth attached to the back side surface of the inner rail of each nozzle segment. The supplemental seal extends from the back side surface of the inner rail for engagement against a first surface of the nozzle support ring at a location radially inwardly of the chordal hinge seal. The high pressure compressor discharge air in the high pressure region of the turbine biases the cloth seal against the annular surface of the nozzle support ring.
Particularly, the cloth seal and shims are secured along a support bracket, the supplemental seal being secured along the back side surface of the inner rail, preferably by welding. Each seal segment extends linearly in a chord-wise direction relative to the turbine axis and is provided in lengths corresponding to the circumferential extent of each inner rail. The supplemental seal segments are also secured along their end edges to the end edges of the inner rail.
The cloth and shims of each seal are shaped to project generally radially inwardly, turn in an axial direction toward the nozzle support ring passing inwardly of the inner rail, and turn again in a generally radial inward direction to form a distal leg on the inner end portion of the seals. The shims in the leg of each seal are slit back from their distal edge to form a plurality of fingers. The fingers of one shim leg overlie the slits between the fingers of the other shim leg. That is, the slits of the shims are staggered in a chord-wise direction relative to one another such that the slits of each shim leg are effectively sealed by the fingers of the opposing shim leg. The slits afford flexibility to the sealing surface of the supplemental seal leg.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and a radially inwardly extending inner rail having a second surface in axial opposition to the first surface, a seal depending from a side surface of the inner rail remote from the second surface and extending radially inwardly of the inner rail for sealing engagement against the first surface to form a seal therebetween, the seal including a seal segment having at least a first plate, an overlay of a woven metallic cloth and a distal margin covered by the cloth and engaging the first surface and a support bracket extending along at least a portion of one side of the seal body to support the seal segment on a side thereof remote from the inner rail, the margin of the seal segment being flexible and preloaded to seal against the first surface.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a plurality of turbine nozzle segments each having at least one stator vane and a radially inwardly extending inner rail having a second surface in axial opposition to the first surface, a seal comprised of a plurality of seal segments each depending from a side surface of the inner rail remote from the second surface and extending radially inwardly of the inner rail for sealing engagement against the first surface to form a seal therewith, each seal segment including a first plate, an overlay of a woven metallic cloth and a distal margin covered by the cloth and engaging the first surface and a plurality of support brackets extending along one side of the seal segments to support the seal bodies on a high pressure side thereof, the margins of the seal bodies being flexible and preloaded to seal against the first surface.